Detection units or instruments are used in a wide variety of different fields to detect the presence of a gas or the presence of a gas in a particular amount. The gas is oftentimes hazardous in nature so that its presence in a particular area can pose a significant health risk. Underground parking garages, for example, are susceptible to the accumulation of potentially dangerous levels of carbon monoxide as a result of vehicular travel in the garage. Similarly, manufacturing facilities that utilize or produce harmful gases in connection with the production of products or in other contexts are susceptible of potential problems should a leak develop in the gas delivery system. Underground mines, manholes and other confined space entries represent other contexts in which similar concerns arise.
In these as well as a wide range of other settings, it is important to be able to determine the existence of the gas or potentially harmful levels of the gas and for this reason appropriate gas detecting instruments are utilized. When the level of gas in the area reaches a certain level, the instrument provides an appropriate indication such as by emitting a noise or providing some other suitable signal.
These instruments, which typically include their own suction pump, require regular calibration to ensure proper and accurate operation. This typically entails the use of a calibration gas which is introduced into the instrument. At present, there are several different techniques employed for calibrating an instrument through use of a calibration gas. One mechanism involves the use of a sample bag into which a desired amount of calibration gas is transferred from the calibration gas source (e.g., gas cylinder). The sample bag containing the calibration gas is then connected to the instrument to be calibrated. The suction pump associated with the instrument draws the calibrated gas out of the sample bag and into the instrument to be calibrated to thereby permit calibration of the instrument. Unfortunately, the use of a sample bag presents a variety of disadvantages and drawbacks.
In one respect, it is typically necessary to employ some additional piece of equipment such as a regulator to transfer the gas from the gas source to the sample bag and this of course requires additional equipment. Also, while calibration gas is being transferred to the sample bag, care must be taken to prevent contamination of the calibration gas. Typically, this sample bag is repeatedly purged in an attempt to cleanse the bag, but this results in gas being wasted.
In addition, it is not uncommon for the sample bag to become ripped or torn, or to simply wear out rather regularly. This adds to the cost associated with this type of calibration procedure. Operator training is also important since the operator must perform a variety of manual steps to prevent contamination and ensure accurate calibration of the instrument. This training can be expensive and time consuming, and still may not eliminate the possibility of contamination or inaccurate calibration.
Another way of effecting the necessary calibration involves permitting calibration gas to flow from the calibration gas cylinder into a "T" at a rate that exceeds the requirement of the instrument to be calibrated. One leg of the "T" is left open to the atmosphere to vent the excess gas while the other leg of the "T" is connected to the instrument to be calibrated. The instrument pump then pumps the gas into the instrument so that the instrument can be calibrated.
This technique also suffers from the disadvantage that additional equipment such as a regulator is required to transfer the gas from the calibration gas cylinder to the instrument. Also, care must once again be taken to prevent contamination in the transfer process and if the flow rate is not higher than the instrument demand, an error in calibration can arise. Also, since the rate of flow of the calibration gas exceeds the instrument requirements, calibration gas is needlessly wasted. Further, the operator must activate and deactivate the calibration gas delivery system to effect calibration of the instrument.
In light of the foregoing, a need exists for a way of calibrating an instrument in a way that addresses the foregoing disadvantages and drawbacks. In one respect, it would be desirable to provide a way of calibrating instruments that eliminates the relatively complex operator training associated with other known calibration techniques. A need also exists for a mechanism that facilitates the transfer of calibration gas from the calibration gas source to the instrument to be calibrated without needlessly wasting calibration gas. It would also be desirable to provide a mechanism that provides the possibility for unattended automatic instrument calibration.